Tanning material and process of preparing the same.



UNITED STATES PATENT orrronv HENRY HICKS HURT, OF COVINGTON, VIRGINIA, ASSIGNOR TO ROBESON PROCESS COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY.

TANNING MATERIAL AND PROCESS OF PREPARING THE SAME.

No Drawing.

To all whom it may concern.

Be it known that I, HENRY HIoKs HURT, a citizen of the United States, residing at Covington. in the county of -Allegh'any and State of Virginia, have invented certain new and usefullmprovements in Tanning Materials and Processes of Preparing Same, of which the following is a specification.

This invention relates to tanning materials and processes of. preparing same; and it relates more particularly to a process of preparing'so-called tanning extracts from a concentrated sulfite waste liquor preparation, in 'which said concentrated liquor preparation is first treated with sulfuric acid in amount sufiicient toprecipitate the major portion but not all of the lime present in said liquor preparation, and is then treated with a soluble bisulfate in amount sufiicient to precipitate substantially all the-remainder of the lime present in the liquor; and the invention relates also to the tanning material or extract resulting from such process, and particularly to a tanning extract thus obtained which contains free lignosulfonic acid or acids but substantially no free mineral acid, said material being acid to litmus and phenolphthalein but substantially not acid to Congo red; all as more fully herein- Y after set forth and as claimed.

In the manufacture of wood pulp for paper making purposes by the so-called sulfite process, comminuted wood'or other cellulosic material is digested with solutions containing bisulfites, such'as bisulfite of calcium or a mixture of calcium and magnesium bisulfites, usually withsome free sulfurous acid, until the soluble or non-cellulosic constituents of the Wood, which are usually grouped under the broad term of lignones, are dissolved, leaving substantially pure cellulose to be subsequently worked up into paper stock. The exact nature of the compounds formed by the interaction of the soluble lignones of the wood with the bisulfites present in the digesting solution is not well understood, but it'is'generally believed that said compounds are, or are in the nature of, lignosulfonates of the bases employed; that is, salts of what are by common consent usually termed lignosulfonic acids. These so-calledlignosulfonic acids, when in free or uncombined condition, are highly eifi'cient tanning agents, be-

Specification of Letters Patent,

Patented JulyZfi, 19115.

Application filed February 26, 1914. Serial No. 821,207. v

ing particularly useful for their plumping effect. In the liquor as it comes from the digesters, however, these lignosulfonic acids are largely combined with lime, and the presence of this base is very disadvantageous in a tanning extract both because of its injurious effect on the hides to be treated, and also because it serves to hinder and prevent the activity of the ligno'sulfonic acids as tanning agents. The problem is therefore to get rid of the lime, to set free a large proportion of the lignosulfonic acids, and to cessive plumping of the hides.

The raw sulfite waste liquor coming from the wood digesters is a rather dilute solution of lignosulfonates,largely lime lignosulfonates, and is of comparatively low specific gravity, being ordinarily in the neighborhood of from 2 to 6 or 7 Baum,

or thereabout. It is also acidin reaction,-

often containing free mineral acid. For the purposes of the presentprocess in itsmost advantageous form, this raw sulfite waste liquor as it comes from the digesters is not suitable startingmaterial to employ, as will appear more fully hereinafter. If, however,

this raw waste liquor be first suitably neutralized with lime, and particularly with a dolomitic lime,v and the liquor thus neutralized be then evaporated down in 'vacuo in accordance with the process disclosed in Patent 833,634 to Robeson, a concentrated product of aspecific gravity of about 31 1 or 32 Baum or thereabout may be obtained which is eminently suitable as the starting material for the present process.

Such a concentrated liquor is substantially neutral, is normally very viscous, and contains generally in the neighborhood of 2 per cent. combined lime (CaO).

It has been proposed heretofore to remove the lime from sulfite waste liquor by means of sulfuric acid alone, or by mea of a soluble bisulfate alone, either the furic acid or the bisulfate when added to the n I posed thereby to be precipitated out. lit has it D also been proposed to treat raw sulfite waste liquor as it comes from the digesters with sulfuric acid in conjunction with sodium bisulfate, the amount of sodium bisulfate used being relatively large compared to the amount of sulfuric acid. None of these proposed methods is found to work satis factorily in practice for reasons given below.

In order to obtain a satisfactory tanning extract from sulfite waste liquor, it is very important that the process be conducted in such a manner that there is no necessity for further treating the product after precitating out and removing the lime. if sulfuric acid or an alkali bisulfate, or both,be added to raw or unconcentrated sulfite waste liquor in the proper theoretical proportion to remove the lime and thereby also to set free a certain proportion of lignosulfonic acids,

it is found upon concentrating the treated waste liquor that an acid is inevitably developed during the evaporating process which acts like and probably is sulfuric acid, some of this acid combining with traces of unprecipitated lime still remaining in the liquor to precipitate lime sulfate, While the greater proportion of the acid thus developed remains free, giving the final concentrated product a very decided acid reaction toward the indicator Congo red, thus indi cating the presence of a mineral acid. Such a product is ordinarily undesirable for use in tanning leather hides or skins for the reason that the sulfuric acid remains in the finished leather and ultimately rots it.

I have also found that it is impractical to treat a concentrated sulfite wast'e liquor product with sulfuric acid alone to precipitate out the lime. It is, of course, very desirable not to diminish the specific gravity of the concentrated sulfite waste liquor preparation any more than is absolutely necessary in precipitating out the lime. Consequently in using sulfuric acid as the precipitant, it is highly desirable to use it in a form of strong commercial acid of say or "66 Baum gravity. I have found, however, that if the theoretical quantity of acid of this strength be added to a concentrated I sulfite waste liquor preparation, the acid does not all combine with the lime, but a substantial proportion thereof attacks the valuable lignosulfonic constituents of the liquor, decomposing and carbonizing or burning them and thereby greatly reducing the percentage of tans in the finished product besides materially deepening its color. Furthermore, where the full theoretical quantity of sulfuric acid is added, even if special precautions be employed to lessen the decomposing and burning action ust demenses scribed, a certain reaction always occurs in which a considerable amount of finely divided or colloidal free sulfur is liberated, together with sulfurous acid, this sulfur rendering subsequent filtration of the liquid entremely difiicult and expensive. Apparently it is only the later portions of the sulfuric acid thus added which act in this undesirable way. The first portions of acid added react selectively or preferentially with the lime compounds in the liquor to form lime sulfate which is precipitated out and to set free lignosulfonic acids. As soon as the proportion of lime compounds remaining in the liquor is reduced below a fairly definite point, the selective action of the acid on the lime compounds seems to cease, and the acid then begins its described attack on the valuable organic constituents of the liquor with liberation of sulfurous acid and free sulfur. If, on the other hand, a soluble bisulfate alone be employed to precipitate the lime from a concentrated product of the character described, while the disadvantages of burning out the tanning constituents and liberating sulfur, etc., are avoided, nevertheless an equally objectionable effect is produced by the introduction of a large quantity of soluble non-tans in the final product; that is, sodium salts of lignosulfonic acid are formed which have comparatively little or no tanning effect and are not absorbed by hide powder to any material extent, and which serve thus merely to greatly increase the ash content of the tanning extract as determined by the usual method of evaporatin a portion of the extract and igniting the residue.

According to the present invention the above diiliculties are avoided by a novel method of reacting under carefully controlled conditions upon a neutral or even it is well to have the liquor somewhat warm.

By using the amount of acid specified and by operating under proper conditions of agitation, this addition of acid produces no decomposition or burning of the organic constituents, and no liberation of sulfur or sul'furous acid to an undesirable exmnt, practically all of the acid reacting with the lime compounds of the liquor to precipitate out calcium sulfate. After the sulfuric acid has been thoroughly mixed with the liquor,

the necessary amount of an alkali bisulfate, advantageously sodium bisulfate, which has been first dissolved in the least possible amount of water, is added to the mixture, this amount being approximately just sufficient to remove the combined lime still remaining in solution. The whole mixture is then best thoroughly stirred for several hours, whereupon the liquor is drawn off and filter pressed to remove the precipitated matter,-chiefly calcium sulfate. The liquid product thus obtained contains alarge proportion of free lignosulfonic acids together with a relatively small proportion of lignosulfonates of soda derived from the sodium bisulfate employed, but contains substantially no lime salts and no mineral acid.

The product reacts acid toward litmus and phenolphthalein, but non-acid to Congo red or in rare instances only faintly acid.

It is evident therefore that sulfite waste liquor or lye properly so-called, that is, the thin raw liquor as it comes from the pulp digesters, is essentially different in its principal characteristics from, and is in no sense equivalent to, the concentrated product which forms the starting material in the present process as actually practised. For the sake of accuracy, therefore,it is convenient to designate the thin raw liquor by its proper name, viz., sulfite waste liquor; while the concentrated product of manufacture is termed a concentrated sulfite waste liquor preparation or product, or simply a concentrated liquor. 0th these ,distinct classes of materials may be generically described as liquors containing valuable organic matter derived from wood in the manufacture of The following detailed typical example will serve to illustrate further the principles of the present process and the character of the new tanning agent obtained thereby: A practically neutral concentrated sulfite waste liquor preparation of about 31 Baum and analyzing about 2 per cent. lime (CaO) content may be run direct from the vacuum pan at a temperature of from 110 to 150 F. into a suitable mixing tankwhich is best equipped with suitable agitating or stirring means. Concentrated liquor of this description weighs about 10.65 pounds per gallon. To the liquor in the tank is added, under constant agitation, approximately 3 per cent. by weight of commercial strong sulfuric acid, usually of about 60 or 66 Baum specific gravity. This acid is best free of iron. When this acid has become thoroughly mixedwith the liquor, about 0.5 percent. by weight of sodium bisulfate, conveniently in the form of ordinary niter cake previously dissolved in as small a quantity of water as possible, is added to the mixture in the tank. It is found in practice that the addition of the sulfuric acid as dewithout further treatment. The extract has a specific gravity of about 29.5 Baum, contains approximately 25 per cent. of tanning substances absorbable by hide powder, and gives an ash residue of about 3.5 per cent.

In practice the material to be treated naturally varies more or less composition and properties from that described in the specific example above which is merely typical of procedure within the scope of the invention. So, also, the composition of the final product obtained may, of course, vary within reasonable limits. It. may be stated, however, that the tanning extract obtained by the present process is characterized by high percentage of tans and by low percentage of non-tans and ash; also by its substantial freedom from calcium compounds, its acidity to litmus and phenolphthalein and non-acidity to Congo red. The ash practically never runs over 4. per cent. and is generally much lower. The specific gravity ordinarily lies between the approximate limits of 28 and 31 Baum.

While "the present process is concerned chiefly with the treatment of a concentrated sulfite waste liquor preparation of the character described, which for most practical purposes is, as stated, a material quite distinct in its characteristic properties from what is commonly termed sulfite waste lye or liquor, which is the raw or unconoentrated liquor as it comes from the pulp digesters, nevertheless it is. novel to treat either sulfite waste liquor or a manufactured product thereof with sulfuric acid and a sulfate, either acid or normal in the manner specified herein, that is, where the proportion of bisulfate used isless than that of the acid and is added after the acid, whereby destruction of valuable organic solubles and formation of colloidal sulfur are substantially precluded. In this respect therefore the invention is not limited to treating a concentrated sulfite waste liquor preparation. The product obtained by treating sulfite waste liquor with these reagents in'the manner'just specified and then concentrating is inferior to that obtained by my regular process above set forth.

Where the term lime is used herein without qualification, it is to be understood -as referring ordinarily to lime combined with lignosulfonic and other acids present in sulfite waste liquor, although the presence of more or less uncombined -l1me is not necessarily intended thereby to be excluded.

While I have particularly described the use of sodium bisulfate, or niter cake, it will of course be understood that I may use, in some cases, normal sodium sulfate in its lieu. But for the reasons stated, the sodium bisulfate used With sulfuric acid in the proportions stated is better. While potassium bisulfate and ammonium bisulfate may be used, I regard the sodium bisulfate as more advantageous. Any indicator possessing the range of.sensitiveness of Congo red may of course be used in its lieu, as for example, methyl orange.

While I have described more particularly the manufacture of a liquid material, it will of course be understood that after its preparation I may further concentrate. T may concentrate it to dryness or to any concentration desired, using any suitable type of evaporating apparatus.

A material possessing a somewhat greater percentage of tanning material for the same concentration may be made by first fermenting away the sugars contained in sulfite waste liquor, thereafter concentrating to the desired degree and treating as above described. The fermentable carbohydrates in sulfite waste liquor are not valuable for tanning.

at I claim is: 1. The process of preparing tanning materials which comprises treatlng a substantially neutral highly concentrated sulfite waste liquor preparation of the character described with sulfuric acid to precipitate therefrom a part of the contained lime and to liberate lignosulfonic acids, precipitating substantially all the remaining contained lime by means of an alkali sulfate, and separating precipitated matter from the mixture, thereby obtaining directly without further concentration aconcentrated tanning material of approm'mately 28 to 31 Baum specific gravity.

2. The process of preparing tanning ma-,

terials which comprises treating a substantially neutral highly concentrated sulfite Waste liquor preparation of the character described with sulfuric acid to precipitate therefrom the major portion of the contained lime, and to liberate lignosulfonic acids, precipitating substantially all the remaining contained lime by means of an alkali bisulfate, and separating precipitated matter from the mixture, thereby obtaining directly Without rther concentration a concentrated tanning material of approximately 28 to 31 Baum specific gravity.

3. The process of prepar ng tanning ma terials which comprises treating a substantially neutral highly concentrated sulfite waste liquor preparation with sulfuric acid menace and sodium bisulfate to precipitatetherefrom substantially all the contained lime and to liberate lignosulfonic acids, the proportions of acid and bisulfate employed being such that the resultant tanning material is acid to litmus and phenolphthalein and substantially non-acid to Congo red and has a specific gravity approximating 28 to 31 Baum.

4. Theprocess of preparing tanning materials which comprises treatmg a substantially neutral highly concentrated sulfite waste liquor preparation of about 30 to 82 Baum specificgravity with strong sulfuric acid in quantlty sufficient to precipitate therefrom nearly all the contained lime and then adding about 0.5 per cent. by weight of sodium bisulfate, and filteringofi the precipitated matter to obtain a finished tanning extract.

6. The rocess of preparing tanning materials whlch comprises adding to a concentrated sulfite waste liquor preparation of high concentration and viscous consistency a sufficient quantity of strong sulfuric acid to precipitate therefrom nearly all the contained lime and to liberate lignosulfonic acids, the liquor being agitated during addition of the sulfuric acid thereto, adding suflicient alkali sulfate to remove substantially all the remaining precipitable lime, continuing the agitation for asuitable period of time, and separating precipitated matter from the treated liquor preparation.

7., The process of preparing tanning material from a concentrated sulfite waste liquor preparation of approximately 30 to 32 Baum density, which comprises adding to such preparation while in a heated condition and with the aid of agitation sufficient strong sulfuric acid to precipitate therefrom all but a relatively small proportion of its. contained lime, a'dding sodium bisulfate to substantiallycomplete the precipitation of lime,

and filtermg ofi' precipitated matter to 010- v cluding substantial destruction of valuable organic solubles in the liquor, and removing the resulting lime-containing precipitate, thereby obtaining directly without further concentration a concentrated tanning material containing free lignosulfonic acids and having a specific gravity of approximately 28 to 31 Baum.

9. The process of preparing a tanning agent from liquors containing valuable organic matter derived from wood in the manufacture of wood pulp by the sulfite process, which comprises adding to such a liquor sufficient strong sulfuric acid to precipitate the major portion of the precipitable lime and to liberate lignosulfonic acids, and then adding a sufficient quantity of an alkali sulfate to precipitate the remainder of the lime, whereby destruction of Valuable organic solubles and formation of colloidal sulfur are substantially avoided.

10. The process of preparing a tanning agent from liquors containing valuable organic matter derived from wood in the manufacture of wood pulp by the sulfite process, which comprises adding to such a liquor sufficient strong sulfuric acid to remove therefrom all but a relatively small portion of the precipitable lime contained therein, and then adding substantially the exact amount of an alkali bisulfate necessary to remove the remainder of such lime, whereby destruction of valuable organic solubles and formation of colloidal sulfur are substantially avoided. I

11. As a new composition of matter, a tanning material in the form of a liquid of about 28 to 31 Baum specific gravity, said liquid comprising substantially all the organic solubles of sulfite Waste liquor valuable for tanning, being acid to litmus and phenolphthalein but substantially non-acid to Congo red, and yielding substantially not more than about 4 per cent. ash residue on ignition.

12. As a new composition of matter, a tanning material of relatively high concentration containing free lignosulfonic acid, said material being substantially free of calcium compounds and being substantially non-acid to Congo red though acid to litmus and phenolphthalein.

In testimony whereof, I affix my signature in the presence of two subscribing witnesses.

HENRY HICKS HURT.

Witnesses:

CHAs. E. HILL, IRA DEW. 

